// ----------------------------------------------------------------------
// <copyright file="CRC.cs" company="none">

// Copyright (C) 2012
//
//   This program is free software: you can redistribute it and/or modify
//   it under the terms of the GNU General Public License as published by 
//   the Free Software Foundation, either version 3 of the License, or
//   (at your option) any later version.
//
//   This program is distributed in the hope that it will be useful, 
//   but WITHOUT ANY WARRANTY; without even the implied warranty of
//   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//   GNU General Public License for more details. 
//
//   You should have received a copy of the GNU General Public License
//   along with this program.  If not, see <http://www.gnu.org/licenses/>. 
//
// </copyright>

// <author>pleoNeX</author>
// <email>benito356@gmail.com</email>
// <date>24/06/2012 14:45:49</date>
// -----------------------------------------------------------------------
using System;
using System.Collections;
using System.IO;
using System.Text;

namespace Ekona.Helper
{
    public static class CRC16
    {
        public static UInt32 Calculate(byte[] bytes, UInt32 init = 0xFFFF)
        {
            UInt32 crc = init;

            for (int i = 0; i < bytes.Length; i++)
            {
                crc = (crc >> 8) ^ crc16tab[(crc ^ bytes[i]) & 0xFF];
            }

            return crc;
        }

        private static ushort[] crc16tab =
        {
	        0x0000, 0xC0C1, 0xC181, 0x0140, 0xC301, 0x03C0, 0x0280, 0xC241,
	        0xC601, 0x06C0, 0x0780, 0xC741, 0x0500, 0xC5C1, 0xC481, 0x0440,
	        0xCC01, 0x0CC0, 0x0D80, 0xCD41, 0x0F00, 0xCFC1, 0xCE81, 0x0E40,
	        0x0A00, 0xCAC1, 0xCB81, 0x0B40, 0xC901, 0x09C0, 0x0880, 0xC841,
	        0xD801, 0x18C0, 0x1980, 0xD941, 0x1B00, 0xDBC1, 0xDA81, 0x1A40,
	        0x1E00, 0xDEC1, 0xDF81, 0x1F40, 0xDD01, 0x1DC0, 0x1C80, 0xDC41,
	        0x1400, 0xD4C1, 0xD581, 0x1540, 0xD701, 0x17C0, 0x1680, 0xD641,
	        0xD201, 0x12C0, 0x1380, 0xD341, 0x1100, 0xD1C1, 0xD081, 0x1040,
	        0xF001, 0x30C0, 0x3180, 0xF141, 0x3300, 0xF3C1, 0xF281, 0x3240,
	        0x3600, 0xF6C1, 0xF781, 0x3740, 0xF501, 0x35C0, 0x3480, 0xF441,
	        0x3C00, 0xFCC1, 0xFD81, 0x3D40, 0xFF01, 0x3FC0, 0x3E80, 0xFE41,
	        0xFA01, 0x3AC0, 0x3B80, 0xFB41, 0x3900, 0xF9C1, 0xF881, 0x3840,
        	0x2800, 0xE8C1, 0xE981, 0x2940, 0xEB01, 0x2BC0, 0x2A80, 0xEA41,
	        0xEE01, 0x2EC0, 0x2F80, 0xEF41, 0x2D00, 0xEDC1, 0xEC81, 0x2C40,
	        0xE401, 0x24C0, 0x2580, 0xE541, 0x2700, 0xE7C1, 0xE681, 0x2640,
    	    0x2200, 0xE2C1, 0xE381, 0x2340, 0xE101, 0x21C0, 0x2080, 0xE041,
	        0xA001, 0x60C0, 0x6180, 0xA141, 0x6300, 0xA3C1, 0xA281, 0x6240,
	        0x6600, 0xA6C1, 0xA781, 0x6740, 0xA501, 0x65C0, 0x6480, 0xA441,
	        0x6C00, 0xACC1, 0xAD81, 0x6D40, 0xAF01, 0x6FC0, 0x6E80, 0xAE41,
        	0xAA01, 0x6AC0, 0x6B80, 0xAB41, 0x6900, 0xA9C1, 0xA881, 0x6840,
	        0x7800, 0xB8C1, 0xB981, 0x7940, 0xBB01, 0x7BC0, 0x7A80, 0xBA41,
	        0xBE01, 0x7EC0, 0x7F80, 0xBF41, 0x7D00, 0xBDC1, 0xBC81, 0x7C40,
	        0xB401, 0x74C0, 0x7580, 0xB541, 0x7700, 0xB7C1, 0xB681, 0x7640,
	        0x7200, 0xB2C1, 0xB381, 0x7340, 0xB101, 0x71C0, 0x7080, 0xB041,
	        0x5000, 0x90C1, 0x9181, 0x5140, 0x9301, 0x53C0, 0x5280, 0x9241,
	        0x9601, 0x56C0, 0x5780, 0x9741, 0x5500, 0x95C1, 0x9481, 0x5440,
	        0x9C01, 0x5CC0, 0x5D80, 0x9D41, 0x5F00, 0x9FC1, 0x9E81, 0x5E40,
	        0x5A00, 0x9AC1, 0x9B81, 0x5B40, 0x9901, 0x59C0, 0x5880, 0x9841,
	        0x8801, 0x48C0, 0x4980, 0x8941, 0x4B00, 0x8BC1, 0x8A81, 0x4A40,
	        0x4E00, 0x8EC1, 0x8F81, 0x4F40, 0x8D01, 0x4DC0, 0x4C80, 0x8C41,
	        0x4400, 0x84C1, 0x8581, 0x4540, 0x8701, 0x47C0, 0x4680, 0x8641,
	        0x8201, 0x42C0, 0x4380, 0x8341, 0x4100, 0x81C1, 0x8081, 0x4040
        };
    }

    public static class CRC32
    {
        // Code from: http://www.codeproject.com/KB/cs/PngUtil.aspx credits to Paul Young

        /// <summary>
        /// Create the CRC-32 table
        /// </summary>
        private static void CreateCrcTable()
        {
            uint c;
            int k;
            int n;

            for (n = 0; n < 256; n++)
            {
                c = (uint)n;

                for (k = 0; k < 8; k++)
                {
                    if ((c & 1) == 1)
                    {
                        c = 0xedb88320 ^ (c >> 1);
                    }
                    else
                    {
                        c = c >> 1;
                    }
                }
                CrcTable[n] = c;
            }
            IsTableCreated = true;
        }
        static uint[] CrcTable = new uint[256];
        static bool IsTableCreated = false;

        /// <summary>
        /// Calculate the CRC from the buffer
        /// </summary>
        /// <param name="buffer">Data to calculate the CRC32</param>
        /// <returns>4 bytes with the CRC32 code</returns>
        public static byte[] Calculate(byte[] buffer)
        {
            uint data = 0xFFFFFFFF;
            int n;

            if (!IsTableCreated)
                CreateCrcTable();

            for (n = 0; n < buffer.Length; n++)
                data = CrcTable[(data ^ buffer[n]) & 0xff] ^ (data >> 8);

            data = data ^ 0xFFFFFFFF;

            byte b1 = Convert.ToByte(data >> 24);
            byte b2 = Convert.ToByte(b1 << 8 ^ data >> 16);
            byte b3 = Convert.ToByte(((data >> 16 << 16) ^ (data >> 8 << 8)) >> 8);
            byte b4 = Convert.ToByte((data >> 8 << 8) ^ data);

            return new byte[] { b1, b2, b3, b4 };
        }
    }
}
